TM 1-1500-204-23-2
(b) Changing spiral. Before installing a Teflon spiral ring in an external groove, you must change the right-hand spiral of
the ring to a left-hand one, as shown in figure 4-74. As you put the ring into the groove, turn the component in a
clockwise direction. This will tend to contract the ring diameter and will reduce the possibility of damage to the ring.
(c) Single installation. Backup rings may be installed singly if pressure acts on only one side of the seal. In figure 4-75,
the backup ring is installed next to the O-ring and opposite to the pressure force.
(d) Dual installation. When dual backup rings are installed, the split scarfed ends must be staggered, as shown in figure
4-76.
(2) Leather backup rings. Leather backup rings also must be Inspected before reuse for defects. Defective rings must be
discarded. To install a leather backup ring, proceed as follows:
(a) Prepare a solution of distilled water and 0 05-percent sodium dichromate, Federal Specification O-S-595, by weight,
in a vessel which can be heated to and maintained at 1550 ( ±
50) F (68°
(±
2.8°) C.)
(b) Completely submerge leather backup rings in solution, and let soak for a period of not less than 15 minutes.
(c) Remove backup rings from soaking vessel and wipe off excess moisture. Immediately install rings as required in
external seal grooves, with grain (hair) side of backup ring toward side of groove, ensuring that backup ring is well seated
against one side of groove to maintain flatness when drying (see figure 4-77).
(d) Place seal with backup ring installed in drying oven with means provided for air circulation at ambient temperature of
1550 (±
5°) F (680 (. 2. 8 0) C. ) for a period of not less than 25 minutes
(e) Remove from oven and allow to return to room temperature before attempting to install
Figure 4-72. Stretching Teflon Backup Ring
Figure 4-73. Installing Teflon Backup Ring
4-86
